In the manufacture of multiple charge-coupled device (CCD) imager color cameras for broadcast or other applications it is necessary to accurately align one imager with respect to other imagers in cameras. This problem is different for solid-state cameras than for tube-type cameras because they do not use magnetic or electrostatic deflection to determine the position of the scan with respect to the projected image. Imaging tubes can be electrically aligned by adjustment of the scanning currents and voltages as well as by positioning of the yoke in the case of magnetic deflection. The ultimate fine positioning is electronic, thereby eliminating the need for fine mechanical manipulation thus resulting in lower camera cost.
The present approach for alignment of CCD imagers, illustratively described in U.S. Pat. No. 4,323,918 issued on Apr. 6, 1982, in the name of S. L. Bendell, involves highly accurate mechanical alignment within a fraction of a pixel. For example, in some devices the vertical pixel dimension is 20 micrometers and the horizontal is 16 micrometers requiring alignment to within a few micrometers. The basic idea is to align all pixels in each chip exactly with the corresponding pixels in the other chips, therefore, corresponding parts of the image fall on exactly the same spatial pixel position for each imager.
In accordance with the principles of the present invention an alternative means for aligning the individual CCD imagers is provided. It is based on the idea that a one-to-one spatial alignment of pixels is not necessary. An electrical registration is provided to effect an instantaneous alignment of the video outputs of a plurality of imagers so that the video outputs correspond to the same point within a scene.
In accordance with one aspect of the present invention the pixel boundaries from imager-to-imager are not necessarily aligned in an exact spatial correspondence. It has been discovered that this electrical registration may be effected without an exact spatial correspondence between imagers. This can be understood by considering an oversampled scene. This scene will be exactly reproduced by the imager and once low pass filtered will not exhibit any aliasing. Therefore, the reproduced image will be the same for any pixel position but merely shifted in time. Scenes which are undersampled will show aliasing and will therefore be sensitive to pixel centers. However, for most real world imaging, alias scene energy is very low in comparison to valid scene information.